that sounds about right. It all depends on how long you are out when you are out and how often you change your DC? We don't go out much either but when we are I always change DC within 2 hours. This weekend we ended up doing some day trips and were out for some long stretches.....
Order three and see how that goes. YOu can always bring some bulkier diapers along in the car and keep them their in case of an emergency or you are out longer than expected. I try not to leave the house with less than three diapers in the bag. Even if we just run to the store. We are still at the unpredictable explosive poo stage though...

__________________"Obstacles are those frightening things that become visible when we take our eyes off our goals." -Henry Ford

Probably 3 minimum, more if you go out every day and tend to use the diapers in the bag a lot.
We like to keep 2-3 diapers in the bag, depending on how long I think we'll be out. Since I don't wash every day, I have more than that total, however (and of course, I'm an addict, LOL!).

__________________
Heather, mom to two sweet boys: B 9/01 and S 7/05.
At MDC/HC/Pin as Heather30ish and Ebay as NYBookMom. Smoke-free, cat-friendly home!

Generally I'd keep 3-4 in the car and/or bag. We don't usually go out that long, but it's nice to have that many. If I'm planning on the whole day out we bring more- probably closer to 7. I hate being unprepared, lol!